Imide-extended liquid bismaleimide resin

ABSTRACT

The invention is based on the discovery that a remarkable improvement in the performance of bismaleimide thermosets can be achieved through the incorporation of an imide-extended liquid bismaleimide monomer. This imide-extended liquid bismaleimide monomer is readily prepared by the condensation of an appropriate dianhydride with two equivalents of an appropriate diamine to give an amine terminated compound. This compound is then condensed with an excess of maleic anhydride to yield an imide-extended liquid bismaleimide monomer.

RELATED APPLICATION DATA

[0001] This application claims priority to Application Serial No.60/468,017, filed May 5, 2003, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to thermosetting adhesivecompositions, methods of preparation and uses therefor. In particular,the present invention relates to thermosetting compounds andcompositions containing an imide-extended liquid bismaleimide resin.

BACKGROUND OF THE INVENTION

[0003] Adhesive compositions, particularly conductive adhesives, areused for a variety of purposes in the fabrication and assembly ofsemiconductor packages and microelectronic devices. The more prominentuses include bonding of electronic elements such as integrated circuitchips to lead frames or other substrates, and bonding of circuitpackages or assemblies to printed wire boards. Adhesives useful forelectronic packaging applications typically exhibit properties such asgood mechanical strength, curing properties that do not affect thecomponent or the carrier, and thixotropic properties compatible withapplication to microelectronic and semiconductor components.

[0004] The bismaleimides represent one useful class of thermosetcompounds that have been used in the microelectronic packaging industry.Bismaleimides are curable, meaning that they are capable ofpolymerization to yield cross-linked resins. In addition, bismaleimidesmay be homocured in the presence of free radicals or photoinitiators, orcombined with other free-radical curing monomers (e.g., acrylates,methacrylates, syrenics, vinyl ethers, vinyl esters, allyl monomers,olefins, and the like). They may also be cured in the presence ofcomonomers via, Diels-Alder, -ene, and Michael addition mechanisms.

[0005] Commercially available bismaleimide thermoset compositions arenoted for their high modulus, and excellent resistance to thermaldegradation. However, these thermoset compositions are also well knownfor brittleness. The utility of the bismaleimide class of thermosetscould be vastly improved if less brittle formulations could be achievedthat retain the desirable thermal and elastic properties.

SUMMARY OF THE INVENTION

[0006] The present invention is based on the discovery that a remarkableimprovement in the performance of bismaleimide thermosets can beachieved through the incorporation of an imide-extended liquidbismaleimide monomer. This imide-extended liquid bismaleimide monomer isreadily prepared by the condensation of an appropriate dianhydride withtwo equivalents of an appropriate diamine to give an amine terminatedcompound. This compound is then condensed with an excess of maleicanhydride to yield an imide-extended liquid bismaleimide monomer.

[0007] When incorporated into a thermoset composition, the imide-linkedmaleimide monomer described herein reduces brittleness and increasestoughness in the composition, while not sacrificing thermal stability.The imide functional group is one of the most thermally stable groupsknown. Thus, the present invention provides a maleimide functionalizedthermoset composition without thermally labile linkages, therebyproviding superior thermal stability when used as a toughener.

[0008] In one embodiment of the invention, there is provided a liquidimide-extended bismaleimide monomer having the structure:

[0009] In another embodiment, there is provided an adhesive compositionincluding a liquid imide-extended bismaleimide monomer having thestructure set forth above; at least one co-monomer selected from thegroup consisting of acrylates, methacrylates, maleimides, vinyl ethers,vinyl esters, styrenic compounds, and allyl functional compounds; and atleast one curing initiator.

[0010] In another embodiment of the invention, there is provided adie-attach adhesive composition including 2 weight percent to about 98weight percent (wt %) of the liquid imide-extended bismaleimide monomerhaving the structure set forth above based on total weight of thecomposition; 10 wt % to about 90 wt % of at least one co-monomerselected from the group consisting of acrylates, methacrylates,maleimides, vinyl ethers, vinyl esters, styrenic compounds, and allylfunctional compounds, based on total weight of the composition; 0 toabout 90 wt % of a conductive filler; 0.1 wt % to about 5 wt % of atleast one curing initiator, based on total weight of the composition;and 0.1 wt % to about 4 wt %, of at least one coupling agent, based ontotal weight of the composition.

[0011] In still another embodiment, there is provided a method forproducing a liquid imide-extended bismaleimide monomer. Such a methodcan be performed, for example, by contacting 4,4′-bisphenol Adianhydride (BPADA) with a diamine under conditions suitable to form animide having terminal amino moieties; and contacting the terminal aminomoieties with maleic anhydride under conditions suitable to form amaleimide, thereby producing a liquid imide-extended bismaleimidemonomer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 illustrates the preparation of a liquid imide-extendedbismaleimide monomer of this invention.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention is based on the discovery that a remarkableimprovement in the performance of bismaleimide thermosets can beachieved through the incorporation of an imide-extended liquidbismaleimide monomer. In one embodiment, there is provided a liquidimide-extended bismaleimide monomer having the structure (I):

[0014] In the structure set forth above, the C₃₆H₇₂ aliphatic moiety isderived from the hydrogenated dimer diamine Versamine 552 (Cognis), andcan be represented by the following structure:

[0015] Referring to FIG. 1, compound (I) is readily prepared by atwo-step, single-pot synthesis. The first step involves the condensationof a dianhydride (BPADA from General Electric) with dimer diamine(Versamine 552 from Cognis Corporation) to form an amine-terminatedpolyimide. The diamine should be present in at least a slight excess ofthat necessary to form the imide-linked diamine intermediate.

[0016] The second step of the reaction involves the condensation of theremaining amine residues with a slight excess of maleic anhydride toform the maleimide moieties. This second step can be accomplishedemploying techniques well known to those of skill in the art. The moststraightforward preparation of maleimides entails formation of themaleamic acid via reaction of the primary amine with maleic anhydride,followed by dehydrative closure of the maleamic acid with aceticanhydride. A major complication is that some or all of the closure isnot to the maleimide, but to the isomaleimide. Essentially theisomaleimide is the dominant or even exclusive kinetic product, whereasthe desired maleimide is the thermodynamic product. Conversion of theisomaleimide to the maleimide is effectively the slow step and,particularly in the case of aliphatic amines, may require forcingconditions which can lower the yield. Of course, a variety of otherapproaches can also be employed.

[0017] For example, dicyclohexylcarbodiimide (DCC) closes maleamic acidsmuch more readily than does acetic anhydride. With DCC, the product isexclusively isomaleimide. However, in the presence of suitableisomerizing agents, such as 1-HOBt hydroxybenzotriazole (HOBt), theproduct is solely the maleimide. The function of the could be to allowthe closure to proceed via the HOBt ester of the maleamic acid (formedvia the agency of DCC) which presumably closes preferentially to themaleimide. Likely, isomerizing agents such as HOBt add to the isoimideto yield the amic acid ester. If this exhibits any tendency whatsoeverto close to the imide, much less a strong bias for doing so, a route forinterconverting isoimide and imide is thereby established and thethermodynamic product, imide, should ultimately prevail. Thus if theinitial closure of ester formed in the DCC reaction yields any isoimide,or if any isoimide is produced by direct closure of the acid, thesituation will be subsequently “corrected” via conversion of theisoimide to the imide by the action of the active ester alcohol as anisomerizing agent.

[0018] An alternative method for affecting the cyclodehydration ofmaleamic acids is set forth in U.S. Pat. No. 5,973,166, the entirecontents of which are incorporate dherein by reference. This methodutilizes amine salts that can be successfully used to replace the polar,aprotic solvents that have been used for the cyclodehydration ofmaleamic acids. The use of these salts provides competitive reactiontimes and product yields relative to results obtained with polar,aprotic solvents. These salts have the advantage of having no vaporpressure and, therefore, have no possibility to co-distill with thewater produced by the cyclodehydration reaction. Furthermore, such saltscan be tailored to have desirable solubility characteristics (i.e.,soluble in the refluxing azeotropic solvent, but insoluble at roomtemperature) that permit their easy removal from the reaction product.Such salts are not destroyed during the cyclodehydration reaction and,therefore, can be efficiently recycled again and again.

[0019] The liquid imide-extended bismaleimide monomer of the inventionmay be used independently in adhesive compositions, or may be combinedwith other adhesive compounds and resins. In one embodiment, thebismaleimide monomer of the invention may be used as the sole thermosetmonomer of the adhesive composition. In another embodiment, thebismaleimide monomer of the invention may be combined the bismaleimidewith other thermoset monomers to make a fully formulated adhesive. Thus,in one embodiment, there is provided an adhesive composition includingthe liquid imide-extended bismaleimide monomer of structure (I), atleast one co-monomer selected from the group consisting of acrylates,methacrylates, maleimides, vinyl ethers, vinyl esters, styreniccompounds, allyl functional compounds, and the like; and at least onecuring initiator.

[0020] In some embodiments, the liquid imide-extended bismaleimidemonomer is present in the composition from 2 weight percent to about 98weight percent (wt %) based on total weight of the composition. In otherembodiments, the at least one co-monomer typically is present in thecomposition from 10 wt % to about 90 wt % based on total weight of thecomposition.

[0021] The at least one curing initiator is typically present in thecomposition from 0.1 wt % to about 5 wt % based on total weight of thecomposition, and is typically a free-radical initiator. As used herein,the term “free radical initiator” refers to any chemical species which,upon exposure to sufficient energy (e.g., light, heat, or the like),decomposes into two parts which are uncharged, but which each possess atleast one unpaired electron. Preferred free radical initiatorscontemplated for use in the practice of the present invention arecompounds which decompose (i.e., have a half life in the range of 0.01to about 10 hours) at temperatures in the range of about 70° C. up to180° C. Exemplary free radical initiators contemplated for use in thepractice of the present invention include peroxides (e.g., dicumylperoxide, dibenzoyl peroxide, 2-butanone peroxide, tert-butylperbenzoate, di-tert-butyl peroxide,2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, bis(tert-butylperoxyisopropyl)benzene, and tert-butyl hydroperoxide), azo compounds(e.g., 2,2′-azobis(2-methyl-propanenitrile),2,2′-azobis(2-methylbutanenitrile), and1,1′-azobis(cyclohexanecarbonitrile)), and the like.

[0022] The term “free radical initiator” also includes photoinitiators.For example, for invention adhesive compositions that contain aphotoinitiator, the curing process can be initiated by UV radiation. Inone embodiment, the photoinitiator is present at a concentration of 0.1wt % to 5 wt % based on the total weight of the organic compounds in thecomposition (excluding any filler). In a one embodiment, thephotoinitiator comprises 0.1 wt % to 3.0 wt %, based on the total weightof the organic compounds in the composition. Photoinitiators includebenzoin derivatives, benzilketals, α,α-dialkoxyacetophenones,α-hydroxyalkylphenones, α-aminoalkylphenones, acylphosphine oxides,titanocene compounds, combinations of benzophenones and amines orMichler's ketone, and the like.

[0023] In another embodiment of the invention, there are provideddie-attach pastes including 2 weight percent to about 98 weight percent(wt %) of the liquid imide-extended bismaleimide monomer of structure(I), based on total weight of the composition; 10 wt % to about 90 wt %of at least one co-monomer selected from the group consisting ofacrylates, methacrylates, maleimides, vinyl ethers, vinyl esters,styrenic compounds, and allyl functional compounds, and the like, basedon total weight of the composition; 0 to about 90 wt % of a conductivefiller; 0.1 wt % to about 5 wt % of at least one curing initiator, basedon total weight of the composition; and 0.1 wt % to about 4 wt %, of atleast one coupling agent, based on total weight of the composition.

[0024] Fillers contemplated for use in the practice of the presentinvention can be electrically conductive and/or thermally conductive,and/or fillers which act primarily to modify the rheology of theresulting composition. Examples of suitable electrically conductivefillers which can be employed in the practice of the present inventioninclude silver, nickel, copper, aluminum, palladium, gold, graphite,metal-coated graphite (e.g., silver-coated copper, nickel-coatedgraphite, copper-coated graphite, and the like), and the like. Examplesof suitable thermally conductive fillers which can be employed in thepractice of the present invention include graphite, aluminum nitride,silicon carbide, boron nitride, diamond dust, alumina, and the like.Compounds which act primarily to modify rheology include fumed silica,alumina, titania, and the like.

[0025] As used herein, the term “coupling agent” refers to chemicalspecies that are capable of bonding to a mineral surface and which alsocontain polymerizably reactive functional group(s) so as to enableinteraction with the adhesive composition. Coupling agents thusfacilitate linkage of the die-attach paste to the substrate to which itis applied.

[0026] Exemplary coupling agents contemplated for use in the practice ofthe present invention include silicate esters, metal acrylate salts(e.g., aluminum methacrylate), titanates (e.g., titaniummethacryloxyethylacetoacetate triisopropoxide), or compounds thatcontain a copolymerizable group and a chelating ligand (e.g., phosphine,mercaptan, acetoacetate, and the like). In some embodiments, thecoupling agents contain both a co-polymerizable function (e.g., vinylmoiety, acrylate moiety, methacrylate moiety, and the like), as well asa silicate ester function. The silicate ester portion of the couplingagent is capable of condensing with metal hydroxides present on themineral surface of substrate, while the co-polymerizable function iscapable of co-polymerizing with the other reactive components ofinvention die-attach paste. In certain embodiments coupling agentscontemplated for use in the practice of the invention are oligomericsilicate coupling agents such as poly(methoxyvinylsiloxane).

[0027] In some embodiments, both photoinitiation and thermal initiationmay be desirable. For example, curing of a photoinitiator-containingadhesive can be started by UV irradiation, and in a later processingstep, curing can be completed by the application of heat to accomplish afree-radical cure. Both UV and thermal initiators may therefore be addedto the adhesive composition.

[0028] In general, these compositions will cure within a temperaturerange of 80-220° C., and curing will be effected within a length of timeof less than 1 minute to 60 minutes. As will be understood by thoseskilled in the art, the time and temperature curing profile for eachadhesive composition will vary, and different compositions can bedesigned to provide the curing profile that will be suited to theparticular industrial manufacturing process.

[0029] In certain embodiments, the adhesive compositions may containcompounds that lend additional flexibility and toughness to theresultant cured adhesive. Such compounds may be any thermoset orthermoplastic material having a Tg of 50° C. or less, and typically willbe a polymeric material characterized by free rotation about thechemical bonds, the presence of ether groups, and the absence of ringstructures. Suitable such modifiers include polyacrylates,poly(butadiene), polyTHF (polymerized tetrahydrofuran), CTBN(carboxy-terminated butadiene-acrylonitrile) rubber, and polypropyleneglycol. When present, toughening compounds may be in an amount up toabout 15 percent by weight of the maleimide and other monofunctionalvinyl compound.

[0030] Inhibitors for free-radial cure may also be added to the adhesivecompositions and die-attach pastes described herein to extend the usefulshelf life of compositions containing the imide-extended maleimides.Examples of these inhibitors include hindered phenols such as2,6-di-tert-butyl-4-methylphenol; 2,6-di-tert-butyl-4-methoxyphenol;tert-butyl hydroquinone;tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydocinnamate))benzene;2,2′-methylenebis(6-tert-butyl-p-cresol); and1,3,5-trimethyl-2,4,6-tris(3′,5′-di-tert-butyl-4-hydroxybenzyl)benzene.Other useful hydrogen-donating antioxidants include derivatives ofp-phenylenediamine and diphenylamine. It is also well know in the artthat hydrogen-donating antioxidants may be synergistically combined withquinones, and metal deactivators to make a very efficient inhibitorpackage. Examples of suitable quinones include benzoquinone, 2-tertbutyl-1,4-benzoquinone; 2-phenyl-1,4-benzoquinone; naphthoquinone, and2,5-dichloro-1,4-benzoquinone. Examples of metal deactivatorsincludeN,N′-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine;oxalyl bis(benzylidenehydrazide); andN-phenyl-N′-(4-toluenesulfonyl)-p-phenylenediamine. Nitroxyl radicalcompounds such as TEMPO (2,2,6,6-tetramethyl-1-piperidnyloxy, freeradical) are also effective as inhibitors at low concentrations. Thetotal amount of antioxidant plus synergists typically falls in the rangeof 100 to 2000 ppm relative to the weight of total base resin. Otheradditives, such as adhesion promoters, in types and amounts known in theart, may also be added.

[0031] These compositions will perform within the commerciallyacceptable range for die attach adhesives. Commerically acceptablevalues for die shear for the adhesives on a 80×80 mil² silicon die arein the range of greater than or equal to 1 kg at room temperature, andgreater than or equal to 0.5 kg at 240° C. Acceptable values for warpagefor a 500×500 mil² die are in the range of less than or equal to 70 Nmat room temperature.

[0032] The coefficient of thermal expansion (CTE) is the change indimension per unit change in temperature for a given material. Differentmaterials will have different rates of expansion. If the CTE is verydifferent for elements attached together, thermal cycling can cause theattached elements to bend, crack, or delaminate. In a typicalsemiconductor assembly, the CTE of the chip is in the range of 2 or 3ppm/° C.; for organic circuit board substrate, the CTE is greater than30 ppm/° C.; therefore, the CTE of the adhesive is best between that ofthe substrate and die.

[0033] When a polymer is subjected to the application of heat, it willmove through a transition region between a hard, glassy state to a soft,rubbery state. This region is known as the glass transition region orTg. If a graph of expansion of the polymer versus temperature isplotted, the glass transition region is the intersection between thelower temperature/glassy region coefficient of thermal expansion and thehigher temperature/rubbery region coefficient of thermal expansion.Above this region, the rate of expansion increases significantly.Consequently, it is preferred that the glass transition of the polymerbe higher-than-normal operating temperatures experienced during theapplication. Alternatively, if the modulus of the polymer bondingmaterial is low enough then the adhesive can adsorb most of the stressesinduced by the thermal expansion mismatches between the chip andsubstrate.

[0034] In yet another embodiment of the invention, there are providedassemblies of components adhered together employing the above-describedadhesive compositions and/or die attach pastes. Thus, for example,assemblies comprising a first article permanently adhered to a secondarticle by a cured aliquot of the above-described adhesive compositionare provided. Articles contemplated for assembly employing inventioncompositions include memory devices, ASIC devices, microprocessors,flash memory devices, and the like.

[0035] Also contemplated are assemblies comprising a microelectronicdevice permanently adhered to a substrate by a cured aliquot of theabove-described die attach paste. Microelectronic devices contemplatedfor use with invention die attach pastes include copper lead frames,Alloy 42 lead frames, silicon dice, gallium arsenide dice, germaniumdice, and the like.

[0036] In accordance with still another embodiment of the presentinvention, there are provided methods for adhesively attaching twocomponent parts to produce the above-described assemblies. Thus, forexample, a first article can be adhesively attached to a second article,employing a method including:

[0037] (a) applying the above-described adhesive composition to thefirst article,

[0038] (b) bringing the first and second article into intimate contactto form an assembly wherein the first article and the second article areseparated only by the adhesive composition applied in (a), andthereafter,

[0039] (c) subjecting the assembly to conditions suitable to cure theadhesive composition.

[0040] Similarly, a microelectronic device can be adhesively attached toa substrate, employing a method comprising:

[0041] (a) applying the above-described die attach paste to thesubstrate and/or the microelectronic device,

[0042] (b) bringing the substrate and the device into intimate contactto form an assembly wherein the substrate and the device are separatedonly by the die attach composition applied in (a), and thereafter,

[0043] (c) subjecting the assembly to conditions suitable to cure thedie attach composition.

[0044] Conditions suitable to cure invention die attach pastes includesubjecting the above-described assembly to a temperature of less thanabout 200° C. for about 0.5 up to 2 minutes. This rapid, short durationheating can be accomplished in a variety of ways, e.g., with an in-lineheated rail, a belt furnace, or the like.

[0045] In still another embodiment of the invention, there is provided amethod for producing a liquid imide-extended bismaleimide monomer. Sucha method can be performed, for example, by contacting 4,4′-bisphenol Adianhydride (BPADA) with a diamine under conditions suitable to form animide having terminal amino moieties; and contacting the terminal aminomoieties with maleic anhydride, thereby producing a liquidimide-extended bismaleimide monomer.

[0046] The following examples are intended only to illustrate thepresent invention and should in no way be construed as limiting thesubject invention.

EXAMPLES Example 1 Synthesis of Liquid Imide-Extended BismaleimideMonomer

[0047] Toluene (350 ml) was added to a one liter round bottom flaskequipped with a Teflon coated stir bar. Triethylamine, 50 g (˜0.50 mole)was added to the flask followed by the slow addition of 50 g (0.52 mole)of anhydrous methanesulphonic acid. The mixture was allowed to stir atroom temperature approximately 10 minutes, followed by the addition of90 g (0.17 mole) of Versamine 552 (dimer diamine, Cognis Corporation).To the mixture was added 41 g (0.08 mole) of BPADA (4,4′-bisphenol-Adianhydride, GE Plastics). A Dean-Stark trap and condenser were attachedto the flask, and the mixture was heated to reflux. After approximatelytwo hours the expected amount of water was collected corresponding tothe complete conversion to the amine terminated diimide. The mixture wasallowed to cool down to below 40° C., and 22 g (0.23 mole, ˜20% excess)of crushed maleic anhydride was added to the flask, followed by theaddition of an extra 10 g of anhydrous methanesulphonic acid. Themixture was again slowly heated to reflux. Approximately 18 hours ofreflux were required to collect the expected amount of water in theDean-Stark trap. After cooling down to room temperature an extra 200 mlof toluene was added to the flask; the stirring was stopped at thispoint and the mixture was allowed to separate. The upper (toluenesolution) fraction was carefully decanted into a 2 liter Erlenmeyerflask. The salt was washed with toluene (2×500 ml) the rinses were alsodecanted and combined. The amber solution was allowed to settleovernight to allow sufficient time for more salt and acid to separatefrom the combined toluene solution. The solution was then filteredthrough a glass-fritted funnel tightly packed with 65 g of silica gel.Following filtration the silica gel was washed with an extra 100 ml oftoluene. The toluene was removed under reduced pressure to provide acrude yield of 120 g (˜85% crude yield) of a dark amber viscous fluid.Thermogravimetric analysis of this product (10° C./min. in air)indicated that there was less than one-half percent weight loss by 300°C. and an onset for decomposition at 454° C. Compound of structure (I)is then isolated by routine analytical techniques, well-known to thoseskilled in the art.

Example 2 Tensile Adhesion Test Results for the Liquid Imide-ExtendedBismaleimide

[0048] Tensile adhesion testing was done on some of the product fromExample 1 The only component added to the test resin was 2% by weight ofdicumyl peroxide initiator. The catalyzed resin mix was then used toaffix aluminum studs to copper slugs. The aluminum posts had a contacthead diameter of 290 mils. The copper slugs had dimensions of1000×400×150 mils. Ten of these test assemblies were constructed foreach of the catalyzed resin mixtures. The parts were cured for thirtyminutes in an oven at 200° C. The Parts were then allowed to cool toroom temperature and the adhesive strength was determined using aSebastian III tensile tester. A control composition was also run alongside the test mixtures. The control mix used was the bismaleimidederived from the dimer diamine (i.e. Versamine 552) also catalyzed with2% dicumyl peroxide. TABLE 1 Tensile Adhesion Test Results Stud PullValue (pounds force) Part Example 1 Control  1 66 23  2 54 16  3 57 15 4 75 12  5 47 19  6 71 9  7 52 22  8 70 18  9 63 8 10 77 6 Average 6315 F_(n−1) 10 6

[0049] The liquid bismaleimide rubber from Example 1 had more than fourtimes the average adhesion of the corresponding control. While notwishing to be bound by theory, it is believed that the improvement seenhere is a direct result of the reduced cross-link density and/or reducedcure shrinkage of the invention composition versus the BMI derivedsolely from the dimer diamine.

[0050] While the invention has been described in detail with respect tothese specific examples, it is understood that modifications andvariations are within the spirit and scope of that which is describedand claimed.

What is claimed is:
 1. A liquid imide-extended bismaleimide monomerhaving the structure:


2. An adhesive composition comprising: a) the liquid imide-extendedbismaleimide monomer of claim 1; b) at least one co-monomer selectedfrom the group consisting of acrylates, methacrylates, maleimides, vinylethers, vinyl esters, styrenic compounds, and allyl functionalcompounds; and c) at least one curing initiator.
 3. The adhesivecomposition of claim 2, wherein the liquid imide-extended bismaleimidemonomer comprises 2 weight percent to about 98 weight percent (wt %)based on total weight of the composition.
 4. The adhesive composition ofclaim 2, wherein the at least one co-monomer comprises 10 wt % to about90 wt % based on total weight of the composition.
 5. The adhesivecomposition of claim 2, wherein the at least one curing initiatorcomprises 0.1 wt % to about 5 wt % based on total weight of thecomposition.
 6. The adhesive composition of claim 2, wherein the curinginitiator comprises a free-radical initiator or a photoinitiator.
 7. Adie-attach paste comprising: a) 2 weight percent to about 98 weightpercent (wt %) of the liquid imide-extended bismaleimide monomer ofclaim 1, based on total weight of the composition. b) 10 wt % to about90 wt % of at least one co-monomer selected from the group consisting ofacrylates, methacrylates, maleimides, vinyl ethers, vinyl esters,styrenic compounds, and allyl functional compounds, based on totalweight of the composition; c) 0 to about 90 wt % of a conductive filler;d) 0.1 wt % to about 5 wt % of at least one curing initiator, based ontotal weight of the composition; e) 0.1 wt % to about 4 wt %, of atleast one coupling agent, based on total weight of the composition. 8.The die-attach paste of claim 7, wherein the coupling agent is asilicate ester, a metal acrylate salt, or a titanate.
 9. The die-attachpaste of claim 7, wherein the conductive filler is electricallyconductive.
 10. The die-attach paste of claim 7, wherein the at leastone curing initiator is a peroxide.
 11. A method for producing a liquidimide-extended bismaleimide monomer comprising: contacting4,4′-bisphenol A dianhydride (BPADA) with a diamine under conditionssuitable to form an imide having terminal amino moieties; and contactingthe terminal amino moieties with maleic anhydride under conditionssuitable to form a maleimide, thereby producing a liquid imide-extendedbismaleimide monomer.
 12. A liquid imide-extended bismaleimide monomerprepared according to the method of claim
 11. 13. An assembly comprisinga first article permanently adhered to a second article by a curedaliquot of the die-attach paste of claim
 7. 14. The assembly of claim13, wherein said first and said second articles comprise memory devices,ASIC devices, microprocessors, or flash memory devices.
 15. A method foradhesively attaching a first article to a second article, comprising:.(a) applying an aliquot of the adhesive composition of claim 2 to thefirst article, (b) bringing the first and second article into intimatecontact to form an assembly wherein the first article and the secondarticle are separated only by the adhesive composition applied in (a),and thereafter, (c) subjecting the assembly to conditions suitable tocure the adhesive composition.
 16. A method for adhesively attaching amicroelectronic device to a substrate comprising: (a) applying the dieattach paste of claim 7 to the substrate and/or the microelectronicdevice, (b) bringing the substrate and the device into intimate contactto form an assembly wherein the substrate and the device are separatedonly by the die-attach paste applied in (a), and thereafter, (c)subjecting the assembly to conditions suitable to cure the die attachpaste.